The criticality of the time on the refund of the projects. The special case of the concession projects

The project management theory, as it has been developed until now, is based on the triptych time–cost–quality. Given that the project's quality is not negotiable, the determinant for the project's efficiency is concerned with the time and the cost, since a possible delay in the construction (time) will result, inter alia (clauses, claims etc.) in a cost's increase. This increase is a result of the extension of the administrative and fixed payments and the differentiation of the project's initial budget which is sure to be increased due to the revisions of the materials and services prices. Led by the effort to detect the above mentioned repercussions on the concession projects and based on mathematical equations that use data relative to the constructional and operational cost of transport infrastructure projects, a research has been made on the variation of the ROE (Return on Equity) for different time parameters of the investment.